There was an AMV Iron Chef years ago, way back at the Santa Clara convention center. They chose 2 editors ahead of time, allowed them to bring their own music, and pre-selected an anime that they weren't told about until they were ready to start the contest (iron chef style). The editing rigs were pre-loaded with all the footage they were allowed to use. It was pretty cool, but I imagine it was fairly costly and complex to arrange everything that way. Still, I'd love to see it done again!